# std::indirect_array

From cppreference.com
< cpp‎ | numeric‎ | valarray

Defined in header `<valarray>` |  |
template< class T > class indirect_array; |  |

`std::indirect_array` is a helper template used by the valarray subscript operator with std::valarray<std::size_t> argument. It has reference semantics to a subset of the array whose indices specified by the std::valarray<std::size_t> object.

### Member types

Type | Definition
`value_type` | `T`

### Member functions

(constructor) | constructs a `indirect_array` (public member function)
(destructor) | destroys a `indirect_array` (public member function)
operator= | assigns contents (public member function)
operator+=operator-=operator*=operator/=operator%=operator&=operator|=operator^=operator<<=operator>>= | performs arithmetic operation on the array referred by indirect array. (public member function)

### Example

Run this code

    #include <iostream>
    #include <valarray>

    int main()
    {
        std::valarray<int> data{0, 1, 2, 3, 4, 5, 6, 7, 8, 9};

        std::valarray<std::size_t> idx{0, 2, 4, 6, 8};

        std::cout << "Original valarray: ";
        for (int n : data)
            std::cout << n << ' ';
        std::cout << '\n';

        data[idx] += data[idx]; // double the values at indices 'idx'

        // the type of data[idx] is std::indirect_array<int>

        std::cout << "After indirect modification: ";
        for (int n : data)
            std::cout << n << ' ';
        std::cout << '\n';
    }

Output:

    Original valarray: 0 1 2 3 4 5 6 7 8 9
    After indirect modification: 0 1 4 3 8 5 12 7 16 9

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/numeric/valarray/indirect_array&oldid=170727"